In the modern dental operatory, handpieces are provided with spot sources of illumination which enable a dentist to observe and operate upon teeth and related structures. A typical handpiece projects one or more light beams laterally from the proximal end of a handle onto a drill, or burr. Light is emitted from a lamp either located in the handle or through fiber optics from a remote light source and transmitted through the handpiece via means of an optical light path that includes a fiber-optic assembly permanently mounted in a handpiece. A particularly desirable handpiece is capable of projecting color-corrected light and is disclosed in U.S. Pat. No. 5,003,434 issued to the assignee of the present application. It is sold under the registered trademark COLORight.RTM..
Most dental handpieces are connected to a delivery system by a tubing which supplies air, water and electricity to a swivel connection. The swivel connection contains a lamp housing assembly adapted to be connected to a dental handpiece which also contains fiber-optics. The tubing and swivel also provide the air and water supply to the handpiece. The swivel enables the handpiece to be readily connected to, and disconnected from, the delivery system for cleaning and sterilization by conventional procedures.
There are several conventional heat sterilization procedures. One procedure involves a so-called chemiclave in which the handpiece is subjected to biocidal chemicals in a hot pressurized environment. The vapor phase of alcohol is used, and a percentage of water (12-15 percent) is always present. In an autoclave the sterilization procedure utilizes water, heat and pressure. The autoclave generates 100% water vapor to which the handpiece is subjected. For instance, in an autoclave, temperatures are developed in a range of 240.degree.-275.degree. F. where super-atmospheric pressures are present. The combination of heat, pressure and moisture (water) causes the degradation of fiber-optic assemblies located in the handpiece.
A major problem with respect to handpiece life is the degradation in the output of light after a fiber-optic handpiece has been subjected to repeated autoclave sterilization cycles. On average, in the chemiclave, fiber-optic handpieces experience an approximately 10% to 20% reduction in light output from as-manufactured conditions after 1200 chemiclave sterilization cycles. In an autoclave, in contrast, there is an approximate 70 percent reduction in light output after 1200 sterilization cycles. Thus, it should be apparent that at least with respect to autoclave sterilized handpieces, the dentist perceives very early in the expected life of the handpiece a decrease in the intensity of light output, and this is obviously very undesirable. The cost to replace some high quality handpiece fiberoptics can be as high as $300, whereas the original cost of this same handpiece may be $600.00.
When one considers that a handpiece should be capable of withstanding over 2000 sterilization cycles with minimal maintenance, a fiber-optic replacement of $300 is far too high in cost to be commercially acceptable. In the case of some endoscopes, coherent viewing fiber-optic assemblies suffer from the same problem and may cost up to $2000 to replace. It should be apparent that there is a real need for a fiber-optic handpiece capable of projecting light over a 2000 autoclave cycle time period and to be able to deliver substantially undiminished light intensity with minimal maintenance.